1. Field of the Invention
This invention relates to a method of using for landfill purposes red mud which is a by-product in the Bayer process of separating alumina from bauxite.
2. Description of the Prior Art
In the Bayer process natural bauxite ore is treated in an alkali solution by heating under pressure to extract the alumina content in solution. In this step, a considerable amount of insoluble residues is released from the bauxite and remain as a "waste" by-product. These residues are commonly known as "red mud" and include fine particles of iron oxides, sodium aluminosilicates, titanium oxides, quartz, etc. The separation and disposal of the red mud from the aluminate liquor is a difficult aspect of the Bayer process.
Thus, because of the fact that red mud consists of very fine particles, a long time is required for settling and separation, using a thickener or the like. The separated red mud is a thick, muddy slurry which contains a considerable amount of alumina and alkali and to recover these valuable components multi-stage washing with a series of thickeners or the like is required. Further, red mud after the washing treatment is in the form of a slurry which still contains some alkali, so that resort to a slurry pump for transporting it from the plant to a disposal site is practically inevitable. The disposal site must be completely enclosed or dammed by an embankment or levee from the standpoint of preventing leakage of the red mud slurry and thus protecting the environment. As the red mud must ordinarily be transported by a slurry pump, the disposal site must be conveniently near to the plant or factory at which it is produced.
It has, of course, been long known to utilize industrial and household waste as a landfill material for reclaiming land which for any of a variety of reasons is unsuited for productive or even recreational purposes. Past attempts to use the recovered red mud in this way have proved unsuccessful. The red mud slurry is very weak and requires in mechanical strength at least several weeks of open exposure before it becomes capable of supporting the weight of humans without danger even in a region having little rainfall. Furthermore, heavy vehicles can never enter such an area, so that it cannot be directly used for construction purposes. (See for example, "Dewatering Large Volume Aqueous Slurries: Sand Bed Filtration of Bauxite Residue" by Vogt, M. E., Stein, D. L., A.I.M.E. Symposium in Las Vegas, Nev. (1976).)